This invention relates to a process for the manufacture of N-chloroimides. The principal prior art processes for preparing N-chloroimides customarily have involved the use of an aqueous system. In general, such prior art processes for preparing N-chloroimides can be classified as follows:
(1) Chlorination of the corresponding imide using an inorganic hypochlorite in a mixture of acetic acid and water; PA1 (2) Chlorination by passing chlorine into an aqueous solution comprising equivalent amounts of the corresponding imide and a strong base, e.g., sodium hydroxide or potassium hydroxide; PA1 (3) Chlorination of the corresponding imide using t-butyl hypochlorite in a mixture of t-butyl alcohol and water. PA1 (1) ability to generate its hydrochloride salt by reaction with the protonated N-chloroimide intermediate; and PA1 (2) generation of a hydrochloride salt, the properties of which include
Of the above general methods, only method (2) prescribes the use of chlorine itself in the production of the N-chloroimide. However, due to the fact of the aqueous system, this method has been found to have serious drawbacks. First, chlorine is only very slightly soluble in water. Secondly, and more importantly, it is known that an imide, when present in an alkaline aqueous medium such as would result from potassium or sodium hydroxide and water, undergoes rapid hydrolysis. When, for example, phthalimide is subjected to alkaline aqueous conditions, the following decomposition sequence occurs: ##STR1##
Even more importantly, it has been established [Arthur R. Hurwitz, "Degradation of N-Chlorosuccinimide in Aqueous Solution" , Diss. Abst., B, 28 (3), 971 (1967)] that an N-cloroimide product, when present in an aqueous alkaline medium, such as would be the case under the conditions of chlorination provided by method (2) above, degrades with possible formation of the highly explosive and toxic gas, nitrogen trichloride. The following sequences are postulated for the decomposition of N-chlorosucclinimide: ##STR2##
Non-aqueous processes for preparing N-chloro compounds have been few. A process for preparing N-halo-t-alkyl cyanamides is described in U.S. Pat. No. 2,686,203. This process treats a t-alkyl cyanamide with molecular chlorine in an inert solvent and in the presence of a molar equivalent of a halogen acid acceptor, typically pyridine.
Recently, a method for preparing N-chlorophthalimide under substantially non-aqueous reaction conditions was discovered. The aforementioned deficiencies of an aqueous alkaline medium thus were avoided by this method which involves contacting an alkali metal salt of phthalimide with chlorine under non-aqueous conditions in the presence of a halogenated aliphatic hydrocarbon and at a temperature of from about - 10.degree. C. to about + 40.degree. C. This method is the subject of co-pending Application Ser. No. 690,471 filed May 27, 1976, now U.S. Pat. 4,082,766.
An even more advantageous method for preparing an N-chloroimide has been discovered. This method is the subject of this invention. It employs a substantially non-aqueous medium and permits use of the imide itself as starting material instead of the previously required alkali metal salt. The N-chloroimide is prepared by contacting the corresponding imide with molecular chlorine at a temperature of from about - 10.degree. C. to about +50.degree. C. under substantially non-aqueous conditions and in the presence of (1) an epoxy compound in an amount representing at least about one epoxy moiety per each imide moiety and (2) at least a catalytic amount of a tertiary amine.